Light Exerts Force When It Shines

The force that sunlight exerts on the surface of the Earth isn't very strong: about a billionth of a pound per square inch (half a billionth of a kilogram per square centimeter). But over large surface areas and at closer distances to the sun, this force becomes more noticeable. It's enough to push an entire spaceship off course by hundreds of miles, provided the spaceship is going far enough. Designs for solar sails also plan to capitalize on this radiation pressure, and could even use it to get a boost in speed at the beginning of a mission by entering an orbit close to the sun.